Electrolytic preparation of periodate oxypolysaccharides



Patented Aug. 11, 1953 2,648,629 I ELECTROLYTIC PREPARATION OF PERIO- DATE OXYPOLYSAOCHARIDES William Dvonch and Charles L. Mehltretter, Peoria, 111., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application March 6, 1951, Serial No. 214,193

(Granted under Title 35, U. S. (lode (1952),

sec. 266) 6 Claims.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes throughout the world without the payment to us of any royalty thereon;

This invention relates to the electrolytic preparation of oxygenated polysaccharides by a novel and advantageous variation of the so-called periodate oxidation method. It relates, particularly, to the preparation of such products as periodate oxystarch, periodate oxycellulose, and the like.

The oxidation of polysaccharides, as heretofore carried out with periodates, is characterized by several technological advantages. One of these is the remarkable ease of control and the peculiar homogeneity of the products. For example, the method, applied to starch, results in the production of a dialdehyde-type of product containing a minimum of carboxyl groups. Periodate oxystarch is thus distinct from other oxygenated starches. For this and other reasons familiar to those versed in the art, it is more amenable to further chemical modification and more likely to produce products of predetermined chemical and physical properties than the usual oxygenated starches. The foregoing statements are generally true, also, of oxycellulose produced by means of periodate oxidations.

Heretofore, it has been necessary to employ periodic acid or its salts in relatively large quantities in preparing periodate oxypolysaccharides. This is a distinct economic disadvantage by reason of their high cost.

According to the present invention, We prepare periodate oxypolysacc'harides by employing a minimum, that is to say, substantially catalytic amount of periodic acid, in an electrolytic oxidation system. In our system, the periodic acid passes through a cycle of reduction by chemical reaction with the polysaccharide also present in the system, followed by electrolytic reoxidation. In this manner and through the agency of the electrolytic system, the periodic acid behaves somewhat as a true catalyst in that its oxidative effect is realized many times over in a chemically reactive environment.

The amount of periodic acid required (as iodic acid) is very small compared with that required in the chemical oxidation. The reason for this is that the periodic acid is being continuously regenerated electrolytically in our process. In any event, the amount of iodic acid added to the system is substantially less than equivalent to the polysaccharide being oxidized.

Our process is carried out in a conventional two-compartment cell in which the anolyte and catholyte are separated by a porous partition to impede circulation of the electrolytes. Means may be provided for cooling the cell. In the specific examples which follow, such a cell will be described in more detail. We employ a lead dioxide anode and preferably a lead cathode.

In our process, the anolyte compartment contains the polysaccharide, as for example, starch, cellulose, dextran or the like, and an amount of iodic acid substantially less than equivalent to the polysaccharide. The catholyte is a dilute solution of an acid unreactive to the anode, such as sulfuric acid. The electrolytic oxidation of iodic to periodic acid takes place at the anode, whereupon the polysaccharide is in turn oxidized chemically, the periodic acid being reduced back to iodic acid. The cycle of electrolytic and chemical oxidation continues during the process until the oxidation of the polysaccharide is substantially complete.

The conditions of current density, potential difference, and the electrolytic composiiton required by our process are simply those required for the electrolytic oxidation of iodic acid to periodic acid. In our preferred lead-lead dioxide system, we employ electric current in approximately percent excess of theory, for we have found the current efficiency to be approximately 40 percent.

The extent of oxidation of the polysaccharide corresponds substantially to the amount of periodic acid produced by the electric current, The current is passed through the system, whereby the iodic acid 'is continuously regenerated to periodic acid at the anode, and the current is continued until substantial amounts of the polysaccharide are oxidized. Complete oxidation requires the amount of current which generates substantially the theoretical amount of periodic acid.

After passage of the required amount of electric current, the product may then be recovered from the anolyte. After separation of the anolyte A containing the product, we prefer to allow it to stand without further treatment for several hours in order to permit completion of the oxidative reaction of the periodic acid which is therein present. The product may be filtered from the anolyte, washed and dried, as desired. It will be readily understood that the anolyte may be reusedto oxidize further amounts of polysaccharide.

The temperature rang over which our novel oxidation may be carried out is quite broad. For example, it may vary about C. to 50 C., affording near quantitative yields throughout the entire range. This is 'a distinct advantage'over the prior chemical periodate methods which have proved inefficient and non-selective at temperatures above C.

The following specific examples illustrate-the invention.

EXAMPLES A series of electrolytic oxidations were carried out according to this invention and the products compared with those periodate oxystarches obtainable by prior methods. The results are tabulated below.

No. 1 and No. 2 were prepared according to the present invention as described in detail below.

No. 3 is an oxystar-ch prepared by oxidation with periodic acid, as described by Jackson and Hudson, J. A. C. S. 59, 2049 (1937). No. 4 was prepared according to the methods described by Purves and his coworkers in J. A. C. S. 61, 1290 (1939), 64, 585 (1942), and Paper Trade Journal 115, 75 (1942).

In Examples Nos. 1 and 2, an electrolytic cell was employed consisting of a battery jar 150 mm. in diameter by 150 mm. high. An anode compartment consisted of a Coors porous cup 90 mm. in diameter by 145 mm. high. The anode was lead dioxide coated upon lead, made by oxidizing the lower 60mm. of a 175 mm. by mm. by 2 mm. lead strip in N sulfuric acid at 1.5 amperes for half an hour. The cathode was several turns of a in. O. D. lead tube which also served as a cooling coilto control the anolyte temperature. The anolyte was made up of 30.0 g. cornstarch which had previously been defatted and 10.0 g. iodic acid in 300 ml. water. The catholytewas 1200 ml. of 2 percent sulfuric acid. The catholyte level was made several cm. above that of the anolyte in order to diminish electroendosmosis and diffusion. The anolyte was wellstirred as 3.0 amperes (0.12 ampere per sq. cm.) at 7-8 volts was passed for 8.25 hrs. The addition of octyl alcohol to the anolyte was occasionally necessary to inhibit foaming.

At the end of each electrolysis, the anolyte was poured into a glass beaker and permitted to stand with stirring for several hours to complete the oxidation by the periodic acid present. The oxystarch product was filtered off, resuspended three times in'water, and finally dried by an acetone wash,followed by desiccation over concentrated sulfuric acid. As'may readily be seen from the tabulated data, the oxystarch products of this invention are in each case quite similar to the periodate oxystarches of the prior art.

Table I ANALYSES OF PERIODATE OXYSTARCHES a N. a by ea?- aa?- degrees percent degrees percent 0 percent i All'values on dry basis. Concentration of oxystarch about 2 g. per 100 ml Estimated by oxime' formation using Method A described by Cladding and Purves, Paper Trade Journal, 116 150 (1943) d Based on calcium acetate method described in ref. c.

The procedure of the foregoing example may likewise Joe. employed in .theperiodate oxidation 4 of cellulose substituting a suspension or mass of fibers for the cornstarch.

We claim:

1. Method-* for the preparation of oxypolysaccharides comprising subjecting a polysaccharide material to the effect of substantially catalytic amounts of periodic acid in the presence of a cathode and a lead dioxide anode at a temperature of about from 5 C. to 50 C., passing electric current through the system, said periodic acid being continuously transformed to iodic acid by chemical reaction with the polysaccharide material and said iodic acid being continuously regenerated to periodic acid at the anode, and continuing said electric current until substantial amounts of the polysaccharide are oxidized.

2. Method for the preparation of oxypolysaccharides comprising subjecting a polysaccharide material selected from the group consisting of starch and cellulose to the effect of substantially catalytic amounts of periodic acidin the presence of a cathode and a lead dioxide anode at a temperature of about from 5 C. to 50 C., passing electric current through the system, said periodic acid being continuously transformed to iodic acid by chemical reaction with the polysaccharide material and said iodic acid being continuously regenerated to periodic acid at the anode, and continuing said electric current until substantial amounts of the polysaccharide are oxidized.

3. Method for the preparation of oxypolysaccharides comprising subjecting a polysaccharide material selected from the group consisting of starch and cellulose to the effect of substantially catalytic amounts of periodic acid in the presence of a lead dioxide anode in an anolyte compartment separated by a porous partition from a cathode in an acidic catholyte, at a temperature of about from 5 C. to 50 C., passing electric current through the system whereby the iodic acid resulting from the chemical oxidation of said polysaccharide is continuously regenerated to periodic acid at the anode, and continuing said electric current until substantial amounts of the polysaccharide are oxidized.

4. Processes of claim 3 in which the polysaccharide is starch.

5. Process of claim 3 in which the cathode is composed of lead.

6. Process of claim 5 in which the current is continued until approximately an amount of periodic acid has been generated equivalent to the amount of polysaccharide in the anode compartment.

Reduction (1926), pp. 380-381.

Jackson et al., Journal American Chemical Society, vol. 59 (1937), pp. 2049-50.

Graugaard et al., Journal American Chemical Society, vol. 61 (1939) pp, 1290-91. 

1. METHOD FOR THE PREPARATION OF OXYPOLYSACCHARIDES COMPRISING SUBJECTING A POLYSACCHARIDE MATERIAL TO THE EFFECT OF SUBSTANTIALLY CATALYTIC AMOUNTS OF PERIODIC ACID IN THE PRESENCE OF A CATHODE AND A LEAD DIOXIDE ANODE AT A TEMPERATURE OF ABOUT FROM 5* C. TO 50* C., PASSING ELECTRIC CURRENT THROUGH THE SYSTEM, SAID PERIODIC ACID BEING CONTINUOUSLY TRANSFORMED TO IODIC ACID BY CHEMICAL REACTION WITH THE POLYSACCHARIDE MATERIAL AND SAID IODIC ACID BEING CONTINUOUSLY REGENERATED TO PERIODIC ACID AT THE ANODE, AND CONTINUING SAID ELECTRIC CURRENT UNTIL SUBSTANTIAL AMOUNTS OF THE POLYSACCHARIDE ARE OXIDIZED. 